High-pass branch of a frequency separating filter for ADSL systems

ABSTRACT

The invention relates to a high-pass branch ( 7 ) of a frequency separating filter for ADSL systems comprising inductive components ( 11, 14 ) which dispose of magnet cores made of a soft magnetic amorphous or nanocrystalline. As a result, frequency separating filters are provided which comprise small structural shapes and which have especially beneficial properties in the relevant frequency and temperature range.

This application claims priority to German Application No. 199 26 699.9filed on Jun. 11, 1999 and International Application No. PCT/DE00/01875filed on Jun. 8, 2000.

The invention relates to a frequency separating filter having a low-passbranch for low frequency signals, particularly of analog communicationssystems, and having a high-pass branch for high frequency signals ofdigital communications systems, with multiple inductive componentshaving magnetic cores.

Until now, RM4, RM6, RM8 and other ferrite pot cores made of corematerials such as N27 and N48 were used as magnetic cores. The necessarydistortion factor requirement was achieved in this case by means ofgapping through slots in the magnetic core.

A disadvantage of gapping is that it causes a reduction of the effectiveavailable core permeability to values around 200. To achieve thenecessary useful inductance, low insertion loss in the blocking zone,and the necessary modulation capability, the volume of the high-passbranch having ferrite cores must be designed very large, depending onthe construction, so that high-pass branches produced from ferrite coresoccupy considerable space. Furthermore, high coupling and windingcapacitances and leaked inductance result from the high number of turnsper unit length of the primary and secondary taping of the ferritesolutions due to the low permeability, which could lead to interferenceeffects.

Proceeding from this related art, the invention has the object ofproviding a frequency separating filter whose high-pass branch issuitable for high frequency signals of digital communications systemsand has a low structural volume.

This object is achieved in that the high-pass branch comprises at leastone component having a magnetic core made of an amorphous ornanocrystalline alloy.

Soft-magnetic alloys which are amorphous and nanocrystalline have asignificantly higher permeability than ferrite. It is nonethelessdifficult to produce magnetic cores from a soft-magnetic alloy which isamorphous or nanocrystalline in such a way that the hysteresis loopshave the necessary linearity for use in digital broadband communicationssystems. A high degree of linearity is, however, necessary to fulfillthe requirements placed on the distortion factor. Since, however, themagnetic modulation of the magnetic core falls with increasingfrequencies, deviations from an ideally linear hysteresis loop, whichoccur during large modulations, are harmless for high frequencies.Therefore, it is possible to provide amorphous or nanocrystallinesoft-magnetic alloys for the inductive components in the high-passbranch of the separating filter.

Preferred alloys for use in the high-pass branch of thefrequency-separating filter are the object of the dependent claims.

In the following, the invention is described in detail with reference tothe attached drawing.

FIG. 1 shows an overview of the connection between a local exchange anda user-side network connection;

FIG. 2 shows a frequency-separating filter having a high-pass branch anda low-pass branch;

FIG. 3 shows a diagram which illustrates an example of the dependence ofthe frequency response of the permeability on the thickness of the tapesused for the production of a magnetic core;

FIG. 4 shows a further diagram which illustrates the dependence of thefrequency response of the permeability on the width of a slot introducedinto a magnetic core;

FIG. 5 shows an illustration of the changes in permeability depending onthe temperature in relation to the permeability at room temperature;

FIG. 6 shows an illustration of the frequency response of the lossresistance Rp in the parallel equivalent network diagram of coils whichhave magnetic cores made of an amorphous alloy;

FIG. 7 shows an illustration of the frequency response of the insertionloss of the coils from FIG. 6;

FIG. 8 shows an illustration of the static field initial load capacityof magnetic cores made of various amorphous and nanocrystalline alloys;

FIG. 9 shows a hysteresis loop having nearly ideal linearity; and

FIGS. 10–15 shows exemplary heat treatments.

Since not all of the details of VDSL systems have been established yet,inductive components of ADSL systems in particular are described in thefollowing. According to the current information, it can be assumed thatthe requirements for inductive components of VDSL systems largelycorrespond to those of ADSL systems.

As shown in FIG. 1, the connection between an ADSL-capable digital localexchange 1 and a user-side network connection 2 (ADSL modem) occurs viaa public two-wire line in the ADSL (Asymmetric Digital Subscriber Line)telecommunication system. POTS (Plain Old Telephone System) or ISDN(Integrated Services Digital Network) connections can run simultaneouslywith the ADSL data over the same two-wire line. The separation andtransmission of the low frequency components (POTS, ISDN) and the highfrequency components (ADSL) is effected by frequency separating filters4 which sit at the end of public two-wire line 3.

The high frequency ADSL signals running over the public two-wire line 3are steered by the frequency separating filters 4 into an ADSL branch 5,while the low frequency POTS and ISDN signals are steered by thefrequency separating filters 4 into the POTS/ISDN branches 6,respectively. The frequency separating filters 4 thus comprise ahigh-pass branch 7 and a low-pass branch 8. In the exemplary embodimentshown in FIG. 2, the high-pass branch 7 is formed by a high-passtransformer 9 and high-pass filter components 10 connected downstream toit. The high-pass transformer 9 has three coils 11, wound on a jointmagnetic core, and a capacitor 12 connected between the primary-sidecoils 11. The downstream high-pass filter components 10 comprisecapacitors 13 and a high-pass filter choke 14. The inductors of thehigh-pass transformer 9 and the high-pass filter choke 14 are referredto in brief in the following as the inductive components of thehigh-pass branch 7.

It should be noted that, in addition to the exemplary embodimentillustrated in FIG. 2, further embodiments of high-pass branch 7 areconceivable.

Thus, the inductive components shown here can also be used in otherembodiments of the high-pass branch 7, for example in an elliptical orinverse-Chebyshev high-pass branch 7.

Depending on the transmission system, one differentiates between the DMTsystem (discrete multitone) and the CAP system (carrierless amplitudephase modulation). The codes have effects on the spectral distributionof the magnetization current of the high-pass branch 7 in thefrequency-separating filter 4.

Furthermore, one must differentiate ADSL systems via POTS and ISDN,which have different lower limiting frequencies (POTS: approximately 30kHz, ISDN: approximately 140 kHz). Therefore, in the followingdifferentiation is made between ADSL-POTS splitters and ADSL-ISDNsplitters. Due to the lower limiting frequencies and higher voltageamplitudes in POTS, one obtains a stronger modulation of the inductivecomponents of the high-pass branch 7 with POTS than with ISDN. However,magnetic cores of the inductive components of the high-pass branch 7 mayneither be saturated due to the U_(ac) modulation, nor may they bemodulated to such degree that system-specific properties which aredefined in the applicable norms are no longer fulfilled.

Therefore, the following requirements are placed on the inductivecomponents inserted on both sides of the public two-wire line 3 in thehigh-pass branch 7:

-   -   a) minimum structural volume    -   b) suitability for the transmission code systems        -   DMT        -   CAP        -   QAM/MQAM ((multiple) quadrature amplitude modulation)    -   c) main inductors <2 mH depending on the filter layout,        generally <0.5 mH, preferably <0.1 mH    -   d) AC voltage modulation of inductors        -   at high frequencies by ADSL signals (from 20 kHz, up to 45            Vpp)        -   at lower frequencies by POTS and ISDN signals with typical            levels in accordance with 1TR110 and ETR80    -   e) loops in accordance with ANSI T1E1.413 and ETSI ETR 328    -   f) low core weight and SMD capability    -   g) ring core shape, therefore simpler safety requirements in        accordance with IEC 950    -   h) low insertion loss in the ADSL pass range (currently >30 kHz        (POTS) or >140 kHz (ISDN) at 1.1 MHz, possibly up to 1.8 MHz),        high insertion loss in the ADSL stop range (currently <20 kHz        (POTS) or <100 kHz (ISDN))    -   i) low and monotonic temperature response of the relevant        magnetic characteristics in the range −40° C.–100° C.

The present invention concerns inductive components for the high-passbranch 7 in ADSL-POTS splitters and ADSL-ISDN splitters, which include asmall metal tape core made of an amorphous or nanocrystalline alloyinstead of a ferrite core. This core obtains its properties, whichconform to standards, through an optimized combination of thickness,alloy, and heat treatment in a magnetic field as well as core-technologymanufacturing steps.

A first basic requirement is that the permeability of the core materialsof the inductive components in the high-pass branch 7 remains asconstant as possible over the entire ADSL frequency range. As FIGS. 3and 4 show, this requirement was fulfilled as follows:

Magnetic cores, which are produced from low-permeability (μ<2,500)alloys, are preferably unslotted. The necessary frequency properties areset in this case via the specific electrical resistance ρ of the alloyand the tape thickness d_(Band). As shown in FIG. 3, d_(Band) is to be<30 μm, preferably <20 μm, and as much as possible <17 μm or even lower,so that the permeability of the core materials remains as constant aspossible in the relevant frequency range. As shown in FIG. 5, these μ(f)properties of the heat-treated materials used here remain stable over awide temperature range.

In contrast, if the magnetic cores are produced from higher permeabilityalloys (μ≧2,500, preferably μ≧10,000), the frequency response of thepermeability μ and therefore that of the inductance L can besignificantly improved by introducing a slot of a tailored width, asshown in FIG. 4. The slot width d_(Schlitz) depends in turn on thecombination of alloy/heat treatment. Typical widths are in the rangefrom 1 to 200 μm.

A second basic requirement is that the insertion loss in the high-passbranch 7 is as low as possible over the entire ADSL frequency range, inaccordance with ANSI T1E1.413. For the overall system, comprising twoADSL modems, a_(E) must be <1 dB in the 100 ohm or 135 ohm system,without taking the line into consideration, with a_(E) being theinsertion loss. In this case, the insertion loss decreases withincreasing value of R_(p) for a predetermined wave impedance. In thiscase, R_(p) is the ohmic resistance in the parallel equivalent networkdiagram for the inductive components, which represents the hysteresislosses in the magnetic core and the ohmic copper losses of the taping.In this case, the relationshipR _(p)(f)=2*π² *N ²*(1/ρ_(mech))*(A _(Fe) /l _(Fe))*f ² *B ² /P_(Fe)(f)  (1)applies, with N being the number of turns, ρ_(mech) being the specificdensity of the magnetic core, A_(Fe) being the cross-sectional surfaceof the magnetic core, l_(Fe) being the iron path length, B being themagnetic induction, and P_(Fe)(f) being the frequency response of thespecific overall losses, which in turn depends on the hysteresis andtape properties.

The insertion loss a_(E) depends, in the way described above, solely onthe loss resistance R_(p), above all in the range of lower and middlefrequencies. The low hysteresis losses and the low values of the windingresistance R_(ou), due to the small number of turns necessary, thereforelead to a low insertion loss a_(E) in the lower and middle frequencyrange. At high frequencies, the fact must also be considered thatmetallic ring tape cores allow particularly low scattering inductances,so that a transformer having such a ring tape core is also distinguishedin this case by particularly low insertion loss values and highreflection loss values a_(R). The low winding capacitances, which can beimplemented due to the small number of turns necessary, also lead tofavorable a_(E) and a_(R) values in the range of higher frequencies. Asa result, metallic ring tape cores therefore have particularly goodproperties in this regard in the entire frequency range.

As can be seen from FIGS. 6 and 7, particularly large R_(p) values canbe achieved with the heat-treated magnetic alloys used here, even withvery small iron path lengths, i.e., small core geometries. Furthermore,it was discovered that a reduction of the tape thickness from 30 μm to20 μm, preferably to 17 μm or even less, led to a further increase ofR_(p), without the dimensions of the core being enlarged due to this.

In summary, it can be established that, precisely through thecombination of extremely linear hysteresis loops and thin tapes of theheat-treated alloys used here, which have a high specific electricalresistance, ADSL high-pass branches 7 with particularly small insertionlosses can be produced.

The R_(p) value can be improved even more by coating at least one tapesurface with an electrically insulating medium, which must have a lowrelative permittivity of ε_(r)<10. Another possibility for displacingthe permeability reduction affected by loss is achieved by the definedsetting of the permeability to the lowest possible level within specificboundaries or by introducing a tailored slot. The properties ofinductive components for the high-pass branch 7 which conform tostandards can be achieved best with amorphous alloys based on cobalt,which are almost free of magnetostriction, and with fine crystallinealloys which are practically free of magnetostriction. The latter aretypically referred to as “nanocrystalline alloys” and are characterizedby an extremely fine grain with an average diameter of less than 100 nm,which occupies more than 50% of the material volume. An importantrequirement is that the inductors have a high saturation induction ofB_([s])>0.6 T, preferably >0.9 T, more preferably >1 T, and a verylinear hysteresis loop with a saturation to remanence ratio ofB_(r)/B_(s)<0.2, preferably <0.05. In this connection, thenanocrystalline materials based on iron which are free ofmagnetostriction are distinguished by a particularly high saturationinduction of 1.1 T or more. A list of all of the alloy systemsconsidered and found suitable according to the invention is found below.

The third basic requirement for achieving the properties required in thehigh-pass branch of ADSL-POTS or ADSL-ISDN splitters is a pronouncedlinearity behavior of the hysteresis loops, as is shown, for example, inFIGS. 8 and 9. Such linear hysteresis loops can be achieved, forexample, by the manufacturing procedures described in the following:

The soft-magnetic amorphous tape, produced by means of rapidsolidification technology, with a thickness d<30 μm, preferably <20 μm,more preferably <17 μm, made of one of the alloys listed below, is woundtension-free on special machines into the magnetic core in its finaldimension. Alternatively, magnetic cores could also be considered inthis case which are constructed from a stack of stamped disks made ofthe alloys mentioned.

As already mentioned, the requirements conforming to the standards forthe frequency properties can be fulfilled even better if the tape iscoated on one or two sides with an electrically insulating materialbefore the winding of the magnetic core, particularly before thestamping of the disks.

For this purpose, depending on the requirements for the quality of theinsulating film, an immersion, pass-through, spray, or electrolysismethod is used on the tape. The same effect can, however, also beachieved by immersion insulation of the wound or stacked magnetic core.In the selection of the insulating medium, care should be taken that, onone hand, it adheres well to the tape surface, and, on the other hand,it does not cause any surface reactions which could lead to damage ofthe magnetic properties. For the alloys used in this case according tothe invention, oxides, acrylates, phosphates, silicates, and chromatesof the elements Ca, Mg, Al, Ti, Zr, Hf, and Si have been shown to beeffective and compatible insulators. In this case, Mg was particularlyeffective, which is applied as a liquid preproduct containing magnesiumto the tape surface, and which transforms into a dense film of MgO,whose thickness can be between 50 nm and 1 μm, during a special heattreatment which does not influence the alloy.

During the subsequent heat treatment of the insulated or uninsulatedmagnetic core to set the soft-magnetic properties, it is to bedifferentiated whether the magnetic core is made of an alloy which issuitable for achieving a nanocrystalline structure or not.

Magnetic cores made of alloys which are suitable for nanocrystallizationare subjected to an exactly tailored crystallization heat treatment,which lies between 440° C. and 690° C. depending on the alloycomposition, to achieve the nanocrystalline structure. Typical dwelltimes are between 4 minutes and 8 hours. Depending on the alloy, thiscrystallization heat treatment is to be performed in vacuum or in apassive or reducing protective gas. In all cases, material-specificpurity conditions are to be considered, which are to be produced byappropriate aids such as element-specific absorber or getter materials,depending on the case. At the same time, through an exactly balancedcombination of temperature and time, the fact is exploited that with thealloy compositions used here, the magnetostriction contributions of finecrystalline grain and amorphous residual phase precisely offset oneanother and the necessary freedom from magnetostriction |λ_(s)|<2 ppm,preferably even |λ_(s)|<0.2 ppm, arises. Depending on the alloy andembodiment of the component, annealing is either performed without afield or in a magnetic field lengthwise to the direction of the woundtape (“longitudinal field”) or transverse to this (“transverse field”).In specific cases, a combination of two or even three of these magneticfield configurations may also be necessary in sequence or parallel toone another. Particularly flat and linear loops were achieved if themagnetic cores were stacked up on their faces exactly so that the stackheight was 10 times, preferably at least 20 times, the core outerdiameter and if a strong transverse field was already applied during thecrystallization heat treatment described. As a rule, the hysteresisloops were flatter in this case the higher the transverse fieldtemperature applied, with exceeding the alloy-specific Curietemperatures and the occurrence of non-magnetic phases, such as Feborides, establishing an upper limiting temperature.

The magnetic properties, i.e., the linearity and the slope of thehysteresis loops may—if necessary—be varied within a wide range by anadditional heat treatment in a magnetic field which is parallel to therotational symmetry axis of the magnetic core—i.e., perpendicular to thetape direction. Depending on the alloy and permeability level to be set,temperatures between 350° C. and 690° C. are necessary in this case. Dueto the kinetics of the atomic reorientation procedures, the resultingpermeability values are normally lower the higher the transverse fieldtemperature. Typical characteristic curves of various suitablenanocrystalline magnetic alloys, which express their linearity behavior,can be seen in FIG. 8. This magnetic field heat treatment was eithercombined directly with the crystallization heat treatment or performedseparately. The same conditions applied for the annealing atmosphere asin the crystallization heat treatment for achieving the nanocrystallinestructure.

It has been shown to be particularly good to subject nanocrystallinealloys whose permeabilities lie in the range between p=13,000 andp=20,000 to the following heat treatment. The cores are first heatedfrom room temperature to a temperature which is approximately 450° C. orhigher at a heating rate of 1 to 20 K/min and subsequently, afterreaching the target temperature of 450° C. or somewhat higher, heated toa target temperature of 550° C. to 580° C. at a slower heating rate of0.1 to 1 K/min and/or at a heating rate of 1 to 10 K/min and kept atthis temperature for a period of 0.5 to 3 hours. The cores are thencooled to room temperature at a cooling rate of 1 to 10 K/min. Theentire heat treatment typically occurs in a transverse field with astrength of 800 to 3,500 A/cm. This example of a heat treatment is shownin FIG. 10. It was successfully performed on magnetic cores made of ananocrystalline alloy with the chemical compositionFe_(73.5)Cu₁Nb₃Si_(15.5)B₇, and in other cases. Since the magnetic coreswere highly permeable, i.e., they had a permeability of approximately15,000, they were subsequently magnetically gapped by slots.

For nanocrystalline alloys which have a relatively low permeabilitycompared to the nanocrystalline alloys above, i.e., they havepermeabilities of less than 15,000, the following heat treatment hasbeen shown to be particularly suitable. The magnetic cores are firstheated from room temperature to a temperature of approximately 550° C.at a heating rate between 1 and 20 K/min and subsequently heated to atarget temperature of 580° C. to 650° C. at a heating rate of 0.1 to 3K/min. The magnetic cores are kept at this temperature for a period of0.5 to 3 hours. The cores are subsequently cooled back to roomtemperature at a cooling rate of 1 to 10 K/min. The entire heattreatment is preferably performed in a transverse field with a strengthof 800 to 3,500 A/cm. This example of a heat treatment is shown in FIG.11. The magnetic cores obtained in this way are subsequently to bemagnetically gapped by slots due to their relatively high permeability.This heat treatment was successfully performed on nanocrystalline alloyswith the chemical composition (Fe_(0.98)CO_(0.02))₉₀Zr₇B₂Cu₁, on thealloy Fe₈₄Zr_(3.5)Nb_(3.5)B₈Cu₁, and on the alloy Fe₈₄Nb₇B₉, and inother cases. The first alloy mentioned had a permeability ofapproximately 8,000 in this case, the second alloy mentioned had apermeability of approximately 15,000, and the last alloy mentioned had apermeability of approximately 10,000 in this case.

In magnetic cores made of amorphous materials, the setting of themagnetic properties, i.e., of the curve and slope of the linear flathysteresis loop, is performed by a heat treatment in a magnetic fieldwhich runs parallel to the rotational symmetry axis—i.e., perpendicularto the tape direction of the magnetic core. Through favorable control ofthe heat treatment, the fact is exploited that the value of thesaturation magnetostriction changes during the heat treatment in thepositive direction by an amount which depends on the alloy compositionuntil it reaches the range |λ_(s)|<2 ppm, preferably even |λ_(s)|<0.1ppm. As table 2 shows, this was also achieved when the amount of Xs waswell over this value in the “as quenched” state of the tape. Dependingon the alloy used, flushing of the core either with air or a reducingprotective gas (e.g., NH₃, H₂, CO₂) or a passive protective gas (e.g.,He, Ne, Ar, N₂, CO₂) is important in this case so that neither oxidationnor other reactions may occur on the tape surfaces. Solid-state physicalreactions may also not occur inside the material due to protective gaswhich diffuses in.

The amorphous magnetic cores for the inductive components of thehigh-pass branch 7 of the ADSL-POTS or ADSL-ISDN splitters aretypically, depending on the alloy composition used, heated under anapplied magnetic field at a rate of 0.1 to 10 K/min to temperaturesbetween 220° C. and 420° C., kept at these temperatures between 0.25 and48 hours in the magnetic field, and subsequently cooled back to roomtemperature at 0.1–5 K/min. Due to the temperature dependence of themagnetic moments, the loops achieved in the amorphous alloys wereflatter and more linear the lower the transverse field temperatures. Theever-slower kinetics during the reorientation leads at the same time toan alloy-specific lower limit, which is essentially determined byeconomic considerations, i.e., by 48-hour long annealing.

Due to the demagnetizing fields inside a core stack, which lead to aconsiderable weakening and divergence of the field lines, especiallyflat and linear loops were only achievable if the magnetic cores werestacked on their faces exactly so that the stack height was at least 10times, preferably at least 20 times, the height of the core outerdiameter. Typical characteristic curves which emphasize the linearcharacter of the loops implemented in this case can be seen in FIG. 8.

In some cases, a temperature plateau in the transverse field may also bedispensed with and the magnetic preferential direction may be producedby cooling the magnetic cores in the transverse field. The permeabilitylevel is then set via the cooling rate below the Curie temperature ofthe magnetic material. This type of transverse field heat treatmentafter a preceding annealing treatment is particularly suitable forsetting very high permeabilities. In magnetic cores treated in this way,the frequency properties conforming to the standards can be achievedthrough gapping by means of introducing a slot of a suitable width.

The following heat treatment has been shown to be particularly suitablein high permeability amorphous alloys, with high permeability referringin the following to permeability values which are significantly largerthan 1,500. First, the amorphous alloy is heated from room temperatureto a temperature between 340° C. and 400° C. at a heating rate between60 and 1200 K/hour. In this case, the magnetic cores are left for aperiod of 0.5 to 4 hours at this temperature. Subsequently, the coresare cooled at a cooling rate between 60 K/hour and 240 K/hour to atemperature between 280° C. and 340° C. The magnetic cores are then leftat this temperature for a period of 2 to 6 hours. After achieving thistarget temperature, the magnetic cores are typically subjected to atransverse field with a strength of approximately 1,200 A/cm. Whilemaintaining this transverse field, the magnetic cores are subsequentlycooled to room temperature at a cooling rate of 60 to 300 K/hours. Thefirst temperature plateau, i.e., the temperature plateau in the rangebetween 340° C. and 400° C., is used to dissipate mechanical stresses.The second temperature plateau, i.e., the temperature plateau in therange between 280° C. and 340° C., is used to achieve the uniaxialanisotropy Ku. Since the magnetic cores are “low permeability” incomparison to magnetic cores made of low-magnetostrictionnanocrystalline alloys, they may subsequently remain ungapped. Such aheat treatment was, for example, successfully applied to thecobalt-based alloy CO_(71.7)Fe_(1.1)Mo₁Mn₄Si_(13.2)B₉. The example of aheat treatment just described is shown in FIG. 12.

For magnetic cores made of amorphous alloys which are relatively lowpermeability in comparison to the alloy class just described, i.e.,which have permeabilities which lie in the range of 1,500 or less, thefollowing heat treatment has been shown to be particularly suitable. Inthis case, the magnetic cores are heated to a target temperature betweenapproximately 280° C. and approximately 360° C. at a heating ratebetween 60 K/hour and 1200 K/hour. The magnetic cores are then kept atthis target temperature for a period of 1 to 6 hours and subsequentlycooled back to room temperature at a cooling rate between 60 K/hour and300 K/hour. It should be noted that the entire heat treatment justdescribed is typically performed in a transverse field with a strengthof approximately 1,500 A/cm. This example of a heat treatment is shownin FIG. 13. The heat treatment just discussed was successfully performedon the amorphous cobalt-based alloys having the chemical compositionsCO_(72.5)Fe_(1.5)Mo_(0.2)Mn₄Si_(4.8)B₁₇, on the alloy with the chemicalcomposition CO_(72.8)Fe_(4.7)Si_(5.5)B₁₇, and on the alloy with thechemical composition CO_(55.6)Fe_(6.1)Mn_(1.1)Si_(4.3)B_(16.2)Ni_(16.5).The magnetic cores made of the amorphous alloy first mentioned have apermeability of approximately 1,500 in this case, the magnetic coresmade of the second alloy mentioned have a permeability of approximately1,200 in this case and finally the magnetic cores made of the last alloymentioned have a permeability of approximately 700 in this case. Sincethe magnetic cores are relatively “low permeability” they can remainunslotted.

The following heat treatment has been shown to be particularlyadvantageous for extremely high permeability amorphous cobalt-basedalloys, i.e., for alloys whose permeability is significantly over20,000. First, they are heated from room temperature to a targettemperature between approximately 400° C. and approximately 460° C. at aheating rate between 1 and 20 K/min. The magnetic cores are left for aperiod between approximately 0.5 hours and approximately 3 hours in thiscase. They are then cooled to a temperature which approximatelycorresponds to the Curie temperature T_(C) at a cooling rate betweenapproximately 120 K/hour and approximately 240 K/hour. After reachingthe approximate Curie temperature T_(C), which typically lies at 200° C.to 250° C., depending on the fine composition, a transverse field with astrength of approximately 2,000 A/cm is switched on and the magneticcore is then cooled back to room temperature under the effect of thisfield at a cooling rate of between 0.2 K/min and approximately 2 K/min.This example of a heat treatment is shown in FIG. 14 and has been shownto be particularly effective for alloys with a composition ofCO₆₈Fe_(3.5)Mo_(1.5)Si_(16.5)B_(10.5) andCO_(68.4)Fe_(3.4)Mn_(1.0)Mo_(0.5)Si_(16.5)B_(10.2). Magnetic cores madefrom the alloy first mentioned have a permeability of approximately160,000 in this case, and magnetic cores made of the second alloymentioned have a permeability of approximately 52,000 in this case.

It has also been shown to be advantageous for extremely highpermeability nanocrystalline alloys, i.e., for nanocrystalline alloyswhich have permeabilities of significantly more than 20,000, to performthe following special heat treatment. Magnetic cores made of suchnanocrystalline alloys are first, for example, heated to a targettemperature of approximately 450° C. at a heating rate betweenapproximately 1 and approximately 20 K/min, subsequently further heatedto a temperature of approximately 500° C. at a heating rate betweenapproximately 0.1 and approximately 1 K/min, and then finally heatedfurther to a target temperature between approximately 550° C. andapproximately 580° C. The magnetic cores are then left at this targettemperature for a period between approximately 0.5 hours andapproximately 3 hours. The magnetic cores are subsequently cooled to atemperature of approximately 360° C. at a cooling rate betweenapproximately 1 and approximately 10 K/min. Upon reaching this secondtarget temperature, a transverse field with a strength of approximately2,000 A/cm is switched on and the cores are left at this secondtemperature for a period between approximately 2 hours and approximately6 hours. Subsequently, they are cooled back to room temperature at acooling rate between approximately 1 and approximately 10 K/min whilemaintaining the transverse field. Naturally, due to the extraordinarilyhigh permeability of such magnetic cores, they are again magneticallygapped via slots. This example of a heat treatment is shown in FIG. 15.

Various methods have been successfully investigated for introducing aslot in the magnetic core to set the height and frequency response ofthe effective permeability μ_(eff). Spark erosion, careful sawing, e.g.,with diamond saws, water jet cutting, or cutting by means of a finecutting wheel have been shown to be particularly suitable forintroducing the slot. It has been observed in this case that the qualityof the slot is very decisive in the frequency response of thepermeability and therefore of the insertion loss. Particularly highcutting quality was achieved by means of impregnation of the cut zonewith a low-viscosity artificial resin, which penetrates between the tapelayers of the core due to the capillary effect. In these cases, locallyoccurring excessive losses in the cut zone were comparatively small and,as a consequence, the frequency response of the permeability wassignificantly more constant than for raw cut surfaces.

Following the heat treatment and the introduction of the slot, themagnetic cores are surface passivated, coated, whirl sintered, orencapsulated in a trough, provided with the primary and/or secondarywindings, and possibly glued or embedded in the component housing. Inthis case, there is also the possibility of using a design in so-calledplanar technology. This method is independent of whether the magneticcore is made of amorphous or nanocrystalline material. However, themechanical handling of the annealed nanocrystalline magnetic core mustbe performed with particular care because of its brittleness.

A further manufacturing possibility is that the tape is first subjectedto a transverse field tempering as it passes and is subsequently woundinto the tape core. The further sequence runs as described above.

The magnetic cores produced with these methods then fulfill thefollowing requirements:

-   -   the main inductance of the wound ring tape core is, depending on        the design of the filter choke, in the range from 0.1 to 2 mH,        the main inductance is also less than 100 μH for particular        embodiments of the filter (e.g., elliptical characteristic).    -   The main inductance meets this value even under maximum        alternating modulation for the frequencies established according        to the standards.    -   The linearity error of the hysteresis loop of the core is so low        that the following applies:        -   0.8≦μ (B)/μ (B=0)≦1.2, preferably        -   0.9≦μ (B)/μ (B=0)≦1.1        -   for B=0–0.8*B_(s).    -   The bit error rates achievable in typical user circuits conform        to the norms (ANSI T1E1.413 and ETSI ETR 328).    -   Using amorphous and nanocrystalline magnetic materials, after        balanced transverse field annealing, the typical minimum core        dimensions shown in table 1, for example, result for        predetermined values of the main inductance, with the dimensions        being given in the sequence outer diameter, inner diameter, and        height.

TABLE 1 core core L_(haupt) dimension mass [μH] [mm³] [g] material 5609.8*6.5*4.4 1.2 Co_(72.8)Fe_(4.7)Si_(5.5)B₁₇ 820 9.3*5.5*2.5 0.78Co_(72.8)Fe_(4.7)Si_(5.5)B₁₇ 410 9.8*6.5*4.4 1.2Co_(55.6)Fe_(6.1)Mn_(1.1)Si_(4.3)B_(16.2)Ni_(16.5) 700 6.0*4.0*2.0 0.18Fe_(88.2)Co_(1.8)Zr₇B₂Cu₁ 950 8.0*4.0*4.0 0.87Fe_(73.5)Cu₁Nb₃Si_(15.5)B₇

Similar core dimensions also result upon the use of the other alloyslisted below, which can be used depending on the application.

An array of relationships must be considered in the dimensioning of theinductive components.

The relationshipL=N ²μ_(o)μ_(r) A _(fe) /l _(fe)  (2)applies for the inductive components, with

-   -   L=inductance of the component    -   N=number of turns per unit length    -   μ_(o)=universal permeability constant    -   μ_(r)=permeability of the material    -   A_(Fe)=iron cross-section of the magnetic core    -   l_(Fe)=iron path length of the magnetic core.

From equation (2), it is obvious that the necessary inductance can onlybe achieved with minimum structural volume if the number of turns perunit length, permeability, core cross-section, and iron path length areadjusted to one another. The permeability μ, applicable over the entirerange of the operating frequency, or, for slotted embodiments, theeffective permeability μ_(eff) of the core material is, besides thefavorable ring-shaped geometry, the decisive parameter for the mostcompact possible dimension of the transformer. Depending on which of thefollowing alloys listed is used and how the associated heat treatment isperformed, a permeability range between 500 and more than 100,000 can becovered in a defined way. By introducing a slot into the magnetic core,the lower limit of the permeability can be displaced down to 100 or evenless (see FIG. 4). For the inductive components of the high-pass branch7, the permeability range μ or μ_(eff)<30,000, particularly <2,500, isused, which provides a high degree of flexibility in regard to thedimensioning of the inductive components. The inductive components forthe high-pass branch 7 implemented with these magnetic cores have astrong advantage in volume relative to the slotted ferrite cores due totheir construction and the high saturation induction of the magneticcores.

A fundamental restriction arises in the selection of the core materialfor the inductive components of the high-pass branch 7 in that themagnetic core may not be magnetized near saturation by the high voltageamplitudes U_(ac) (ADSL).

The induction corresponding to the signal modulation is given byB _(ac)=(1/N A _(fe))*∫U _(ac) dt  (3)

The permeability and the distortion factor can only fall very slightlywith this signal modulation. For these reasons, the judgment of thematerial is performed with reference to μ(B_(ac)) and distortion factorcharacteristic curves.

Since the distortion factor rises with increasing amplitude of magneticinduction B, the alloy composition must be determined in combinationwith the transverse field heat treatment so that, on one hand, thesaturation induction is as high as possible, and, on the other hand, thepermeability is below an upper limit dependent on the operatingconditions.

A lower permeability μ or μ_(eff) has an increase of the number of turnsper unit length N and therefore, with a predetermined voltage amplitudeaccording to equation (3), a lower amplitude of magnetic induction B asa consequence, which leads to a better distortion factor.

In the following, suitable alloy systems will now be described moredetail. It was found that with the alloy systems described in thefollowing, if the conditions described above were maintained, inductiveelements for high-pass branches with particularly linear hysteresisloops and small structural shapes could be produced which had all theproperties conforming to the standards.

In the alloy systems listed below, the greater than/less than signsenclose the limits, all at % information should be consideredapproximate.

Alloy System 1:

A first alloy system suitable for high-pass branch 7 has the compositionCo_(a)(Fe_(1−c)Mn_(c))_(b)Ni_(d)M_(e)Si_(x)B_(y)C_(z), with M indicatingone or more elements from the group Nb, Mo, Ta, Cr, W, Ge, and P anda+b+d+e+x+y+z=100, with

-   -   Co: a=40–82 at %, preferably a>50 at %,    -   Fe⁺ Mn: b=3–10 at %,    -   Mn/Fe: c=0–1, preferably c<0.5,    -   Ni: d=0–30 at %, preferably d<20 at %,    -   M: e=0–5 at %, preferably e<3 at %,    -   Si: x=0–17 at %, preferably x>1 at %,    -   B: y=8–26 at %, preferably 8–20 at %,    -   C: z=0–3 at %,    -   15<e+x+y+z<30, preferably 18<e+x+y+z<25.

Alloys of this system remain amorphous after the heat treatment.Depending on the composition and heat treatment, extremely linearhysteresis loops having a very wide permeability range between 500 and100,000 or more can be implemented with this system. To achieve theinductances conforming to the standards, the magnetic cores weremagnetically gapped in some cases by introducing a slot of a suitablewidth.

In this case, it has been shown to be particularly important that thevalue of the saturation magnetostriction can be reliably set toparticularly small values of |λ_(s)|<0.1 ppm with a heat treatmenttailored to the alloy composition. A particularly linear loop shaperesults in this way, which leads to a particularly high consistency ofthe permeability over a wide induction range. In addition, theoccurrence of damaging magnetoelastic resonances of the ring-shaped coreare avoided by this. At specific frequencies of the induction curve,these may lead to breaks of the permeability or to elevated hysteresislosses. During the experiments it was discovered that precisely thecombination of this near freedom from magnetostriction, a tape thicknesswhich was as low as possible (preferably less than 17 μm), and acomparatively high specific electrical resistance of 1.1 to 1.5 μΩmleads to extremely good frequency response, which is particularlysuitable for the ADSL high-pass filter 10 and the ADSL high-passtransformer 9.

Alloy System 2:

A second alloy system has the compositionFe_(a)Co_(b)Cu_(c)Si_(d)B_(e)M_(f), with M indicating an element fromthe group Nb, W, Ta, V, Zr, Hf, Ti, Mo, or a combination of these anda+b+c+d+e+f=100%, with

-   -   Fe: a=100%−b−c−d−e−f,    -   Co: b=0–15% at %, preferably 0—0.5% at %,    -   Cu: c=0.5–2 at %, preferably 0.8–1.2 at %,    -   M: f=1–5 at %, preferably 2–3 at %,    -   Si: d=6.5–18 at %, preferably 14–17 at %,    -   B: e=5–14 at %.        with d+e>18 at %, preferably d+e=22–24 at %. Alloys of this        system had been shown to be very suitable for the ADSL high-pass        branch 7 due to their linear loop shape and their very good        frequency response. Particularly good ADSL high-pass properties        are achieved in the alloy compositions designated with        “preferably,” since in this case, just as in the alloy system 1,        a zero crossing of the saturation magnetostriction may be        achieved. At the same time, it was also found out that precisely        the combination of a high specific electrical resistance of 1.1        to 1.2 μΩm and a low tape thickness led to outstanding frequency        response and therefore outstanding properties of the ADSL        high-pass transformer 9 and the high-pass filter choke 14.

The comparatively high saturation induction for extremely linear loops,measured at B_(s)=1.1—1.3 T, has also been shown to be veryadvantageous, since in this way high induction values of 1 T or evenmore may be modulated. In addition, it was found that the temperaturecharacteristic of the magnetic core may be adjusted in a targeted way bymeans of the heat treatment for setting the permeability. From this,precisely in rough environmental conditions, which can certainly occurin telecommunication devices, advantages specific to an applicationwhich cannot be implemented in other ways may arise. For ring tape coreshaving higher permeability values, gapping by means of a slot was usedto set the properties conforming to the standards.

Alloy System 3:

A third alloy system suitable for high-pass filters has the compositionFe_(x)Zr_(y)Nb_(z)B_(v)Cu_(w), with x+y+z+v+w=100 at %, with

-   -   Fe: x=100 at %−y−z−v−w, preferably 83–86 at %,    -   Zr: y=2–5 at %, preferably 3–4 at %,    -   Nb: z=2–5 at %, preferably 3–4 at %,    -   B: v=5–9 at %,    -   Cu: w=0.5–1.5 at %, preferably 1 at %,        with y+z>5 at %, preferably 6–7 at %,        and y+z+v>11 at %, preferably 12–16 at %.

With alloys of this system, transverse field heat treatments could beperformed alloy-specific in the interval between 550° C. and 650° C.,and linear loop shapes and a good frequency response, suitable for theADSL high-pass filter 10, could be achieved. The high saturationinduction of approximately 1.5 to 1.6 T had a particularly favorableeffect on the size of the component.

Alloy System 4:

A further suitable alloy system has the compositionFe_(x)M_(y)B_(z)Cu_(w), with M indicating an element from the group Zr,Hf, Nb and x+y+z+w=100 at %, with

-   -   Fe: x=100 at %−y−z−w, preferably, 83–91 at %,    -   M: y=6–8 at %, preferably 7 at %,    -   B: z=3–9 at %,    -   Cu: w=0–1.5 at %.

The basic requirement of |λ_(s)|<1 ppm could be fulfilled with alloys ofthis system. The alloy-specific permeabilities achieved with thetransverse field treatments performed between 550° C. and 650° C. wererelatively low, between 2,000 and 15,000. The linearity requirementsnecessary for the ADSL high-pass filter 10 were met above all in thiscase in the upper range of the transverse field temperatures. Very smalldesigns could be implemented due to the high saturation induction of 1.4to 1.5 T.

Alloy System 5:

Finally, a fifth alloy system has the composition(Fe_(0.98)CO_(0.02))_(90−x)Zr₇B_(2+x)Cu₁, with x=0–3, preferably x=0,with the residual alloy component Co able to be replaced by Ni withappropriate equalization.

In this system, a zero crossing in the saturation magnetostriction wasachieved with alloy-specific tailored transverse field heat treatment,which led to particularly linear hysteresis curves. In this way, thefrequency responses of the complex permeability were so greatly improvedthat they came very close to those of alloy systems 1 and 2. The highsaturation induction, which was measured at values of B_(s)=1.65 to 1.75T, was shown to be an outstanding advantage of this system. Through theparticularly favorable combination of near freedom from magnetostrictionand high saturation induction, low-distortion usable inductionamplitudes of up to 1.5 Tesla and more could be implemented, throughwhich particularly small structural shapes, which were to be used bothfor the ADSL high-pass filter choke 14 and for the ADSL high-passtransformer 9, were made possible.

The alloy systems 2 to 5 obtain a fine crystalline structure with graindiameters under 100 nm after the heat treatment. These grains aresurrounded by an amorphous phase which, however, occupies less than 50%of the material volume.

All of the alloy systems 1 to 5 are distinguished by the followingproperties:

-   -   extremely linear hysteresis loops;    -   amount of the saturation magnetostriction |λ_(s)|<2 ppm,        preferably <0.1 ppm after the heat treatment. In the        cobalt-based amorphous materials, the saturation        magnetostriction may be set by fine-tuning the Fe and Mn content        appropriately. In the nanocrystalline alloys, the saturation        magnetostriction can be set via the size of the fine crystalline        grain, which can be produced by a targeted adjustment of the        heat treatment, the metalloid content, and the content of        refractory metals.    -   saturation induction of 0.6 T to 1.7 T, with the saturation        induction able to be fine-tuned by selection of the content of        Ni, Co, M, Si, B, and C.    -   tapes whose thickness can be less than 17 μm;    -   high specific electrical resistance, which can be up to 1.5 μΩm.

The requirements and alloy ranges described above were maintained and/orfulfilled after performing the heat treatment described, e.g., throughthe exemplary alloys listed in table 2.

TABLE 2 anisotropic saturation saturation field magnetostriction λ_(s)induction strength H₃ as heat- Alloy composition [at %] structure [T][A/cm] quenched treated Co_(71.7)Fe_(1.1)Mo₁Mn₄Si_(13.2)B₉ amorphous0.82 1.5 −12*10⁻⁸ −3.5*10⁻⁸ Co_(72.5)Fe_(1.5)Mo_(0.2)Mn₄Si_(4.8)B₁₇amorphous 1.0 3.5 −12*10⁻⁸ −4.1*10⁻⁸ Co_(72.8)Fe_(4.7)Si_(5.5)B₁₇amorphous 0.99 4.8 −32*10⁻⁸ −1.6*10⁻⁸Co_(55.6)Fe_(6.1)Mn_(1.1)Si_(4.3)B_(16.2)Ni_(16.5) amorphous 0.93 8.0−110*10⁻⁸ +4.2*10⁻⁸ Fe_(73.5)Cu₁Nb₃Si_(15.5)B₇ nanocr. 1.21 0.7 −24*10⁻⁶+1.6*10⁻⁷ (Fe_(0.98)Co_(0.02))₉₀Zr₇B₂Cu₁ nanocr. 1.70 1.7 — −1.0*10⁻⁷Fe₈₄Zr_(3.5)Nb_(3.5)B₈Cu₁ nanocr. 1.53 0.8 +3*10⁻⁶ +1.5*10⁻⁷ Fe₈₄Nb₇B₉nanocr. 1.5 1.1 — +1.0*10⁻⁷

The amorphous, fine crystalline, or nanocrystalline alloys listed intable 2 are distinguished by particularly high values of the saturationinduction of up to 1.7 Tesla. This allows comparatively highpermeability values, which produces further advantages in regard tooverall size and taping relative to ferrite transformers.

LIST OF REFERENCE NUMBERS

-   1 local exchange-   2 network connection-   3 public two-wire line-   4 separating filter-   5 ADSL branch-   6 ISDN/POTS branch-   7 high-pass branch-   8 low-pass branch-   9 high-pass transformer-   10 high-pass filter components-   11 coils-   12 capacitor-   13 capacitor-   14 high-pass filter choke

1. A frequency separating filter having a low-pass branch for lowfrequency signals, particularly of analog communication systems, and ahigh-pass branch for high frequency signals of digital communicationsystems, with multiple inductive components with magnetic cores, whereinthe high-pass branch comprises a pass range above about 20 kHz, at leastone component with a magnetic core made of an amorphous ornanocrystalline alloy, and wherein the alloy has the compositionCo_(a)(Fe_(1−c)Mn_(c))_(b)Ni_(d)M_(e)Si_(x)B_(y)C_(z), with M indicatingone or more elements from the group Nb, Mo, Ta, Cr, W, Ge, and P anda+b+d+e+x+y+z=100, with Co: a=40–82 at %, Fe⁺ Mn: b=3–10 at %, Mn/Fe:c=0–1, Ni: d=0–30 at %, M; e=0–5 at %, Si: x=0–17 at %, B: y=8–26 at %,C: z=0–3 at %,15<e+x+y+z<30.
 2. The frequency separating filter according to claim 1,wherein the following relationships apply: Co: a=50–82 at %, Fe+Mn:b=3–10 at %, Mn/Fe: c=0–0.5, Ni: d=0–20 at %, M: e=0–3 at %, Si: x=1–17at %, B: y=8–20 at %, C: z=0–3 at %, with 18<e+x+y+z<25.
 3. A frequencyseparating filter having a low-pass branch for low frequency signals,particularly of analog communication systems, and a high-pass branch forhigh frequency signals of digital communication systems, with multipleinductive components with magnetic cores, wherein the high-pass branchcomprises a pass range above about 20 kHz, at least one component with amagnetic core made of an amorphous or nanocrystalline alloy, and whereinthe alloy has the composition Fe_(a)Cu_(c)M_(f)Si_(d)B_(c), with Mindicating an element from the group Nb, W, Ta, Zr, Hf, Ti, Mo, or acombination of these and a+c+f+d+e=100%, with Fe: a=100%−c−f−d−e, Cu:c=0.5–2 at %, M: f=1–5 at %, Si: d=6.5–18 at %, B: e=5–14 at %, withd+e>18 at %.
 4. The frequency separating filter according to claim 3,wherein the following relationships apply: Cu: c=0.8–1.2 at %, M: f=2–3at %, Si; d=14–17 at %, B: e=5–14 at %, with d+e=22–24 at %.
 5. Thefrequency separating filter according to claim 4, wherein the alloy alsohas Cob with Co: b=0—0.5 at %.
 6. The frequency separating filteraccording to claim 3, wherein the alloy also has an element which is Coor Ni.
 7. The frequency separating filter according to claim 6, whereinthe alloy also has Co_(b) with Co: b=0–15 at %.
 8. A frequencyseparating filter having a low-pass branch for low frequency signals,particularly of analog communication systems, and a high-pass branch forhigh frequency signals of digital communication systems, with multipleinductive components with magnetic cores, wherein the high-pass branchcomprises a pass range above about 20 kHz at least one component with amagnetic core made of an amorphous or nanocrystalline alloy, and whereinthe alloy has the composition Fe_(x)Zr_(y)Nb_(z)B_(v)Cu_(w), withx+y+z+v+w=100 at %, with Fe: x=100 at %−y−z−v−w, Zr: y=2–5 at %, Nb:z=2–5 at %, B: v=5–9 at %, Cu: w=0.5–1.5 at %, with y+z>5 at % andy+z+v>11 at %.
 9. The frequency separating filter according to claim 8,wherein the following relationships apply; Fe: x=83–86 at %, Zr: y=3–4at %, Nb: z=3–4 at %, B: v=5–9 at %, Cu: w=1 at %, with y+z=6–7 at %,and y+z+v>12–16 at %.
 10. A frequency separating filter having alow-pass branch for low frequency signals, particularly of analogcommunication systems, and a high-pass branch for high frequency signalsof digital communication systems, with multiple inductive componentswith magnetic cores, wherein the high-pass branch comprises a pass rangeabove about 20 kHz, at least one component with a magnetic core made ofan amorphous or nanocrystalline alloy, and wherein the alloy has thecomposition Fe_(x)M_(y)B₂Cu_(w), with M indicating an element from thegroup Zr, Hf, Nb and x+y+z+w=100 at %, with Fe: x=100 at %−y−z−w, M:y=5–8 at %, B: z=3–9 at %, Cu: w=0–1.5 at %.
 11. The frequencyseparating filter according to claim 10, wherein the followingrelationships apply: Fe: x=83–91 at %, M: y=7 at %, B: z=3–9 at %, Cu:w=0–1.5 at %.
 12. A frequency separating filter having a low-pass branchfor low frequency signals, particularly of analog communication systems,and a high-pass branch for high frequency signals of digitalcommunication systems, with multiple inductive components with magneticcores, wherein the high-pass branch comprises a pass range above about20 kHz, at least one component with a magnetic core made of an amorphousor nanocrystalline alloy, and wherein the alloy has the composition(Fe_(0.98)Co_(0.02))_(90−x)Zr₇B_(2+x)Cu₁, with x=0–3, with the residualalloy component Co able to be replaced by Ni with appropriateequalization.
 13. The frequency separating filter according to claim 12,wherein x=0.